I have had a very good friend of mine, and the person that I do most of my editing work for, highly recommends this product
http://www.redgiantsoftware.com/product ... luraleyes/
Be sure to check out the video
He says that it will flawlessly sync 100's of clips, audio and video, from 2 or more cameras (doesn't matter how many as long as they have audio) and that it never fails. I was amazed to hear that this was really possible and that it was that accurate but he swears by it. So much so that he will stop and start cameras during a wedding ceremony because he doesn't have to worry about syncing the clips anymore.
[youtube]http://www.youtube.com/watch?v=xNRcjS_t0KI[/youtube]